Abstract:
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Purpose: Recent developments suggest that double contrast MD-CT may provide an alternative to MRI for measuring articular cartilage thickness. We designed a study to investigate this hypothesis.
Methods and Materials: Six fresh-frozen cadaver foot/ankle specimens (average age 55 years) were transected 5 cm superior to the medial malleolus. The specimens were individually mounted in a support/drill guide, made of MRI-compatible plastic. This fixture held the ankle joint under slight distraction. To non-invasively mark locations on the articular surface, an array of very small holes was drilled through the joint from the tibial side. Each specimen was first scanned by MRI using a 3-D SPGR sequence. This was followed by a double contrast arthrogram using 0.3-0.5 ml of Hypaque-60, followed by 7-10 ml of air injected under fluoroscopic guidance. A CT scan was then performed on a 4-detector scanner using 1 mm slice thickness and images were reconstructed at 0.5 mm intervals. Images from both modalities were downloaded to a workstation running Vitrea analysis software and cartilage thickness was measured adjacent to the drill holes. The image contrast parameters (window/level) employed were the same as those used clinically at our institution to image cartilage. The specimens were disarticulated to expose the articular surfaces. Under saline irrigation, a trephine was passed over each marker hole to remove a small core of cartilage and bone. These cores were bisected, mounted on the stage of an optical microscope, and digitally photographed at 40x magnification. The digital images were downloaded to Photoshop, and a superimposed measuring grid was used to determine cartilage thickness.
Results: Location-matched cartilage thicknesses determined by MRI, MD-CT, and physical measurement (the gold standard) were obtained at 88 total sites on 6 cadaver ankle joints. The average thickness as measured by MD-CT was 1.60 mm with a mean absolute error (relative to the gold standard) of 0.12 mm (std dev: 0.10 mm). When the MD-CT thicknesses were regressed against physical, the correlation coefficient (R-squared) was 0.85. The average thickness as measured by MRI was 1.85 mm with a mean absolute error of 0.20 mm (std dev: 0.13 mm). The MRI vs. physical correlation was only 0.47. This increased accuracy of MD-CT over MRI, as evidenced by the absolute error and correlation values, was significant (p < 0.0001, paired t-test).
Conclusion: Cartilage thickness measurements obtained with double contrast MD-CT arthropgraphy are more accurate than measurements obtained by MRI.
Questions about this event email: george-el-khoury@uiowa.edu
El-Khoury MD, G,
Double Contrast MD-CT Arthrography is Superior to MRI in Assessing Cartilage Thickness in the Ankle. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3103311.html
